Magnetic thickness gauge with a gas-supported sensor and a suction source in the base

ABSTRACT

In an apparatus for measuring the thickness of material including a magnetic sensor forming an incomplete magnetic circuit, a gas source, structure defining a gas-confining chamber in communication with said gas source providing a gas cushion on the top surface of said material for supporting the sensor a fixed distance above the top surface of said material, and readout means for producing a signal dependent on relative vertical sensor movement, the improvement comprising material support structure including a supporting member formed of magnetic material to complete a magnetic circuit with the sensor, and providing a flat supporting surface located opposite the sensor and contacting the underside of the material, a suction source, and structure providing communication between the suction source and the underside of the material adjacent said flat supporting surface to maintain the underside of the material flush against the flat supporting circuit such that parameters of the magnetic circuit due to the distance between the sensor and the magnetic supporting member are dependent solely on the thickness of the material.

United States Patent [72] Inventors John J Horn East Greenwich;

George E. Corneau, Central Falls, both of R.I.

[21] Appl. No. 864,130

[22] Filed Oct. 6, 1969 [45] Patented Nov. 2,1971

[73] Assignee Indev, Inc.

Pawtuclret, 11.1.

[54] MAGNETIC THICKNESS GAUGE WITH A GAS- SUPPORTED SENSOR AND A SUCTIONSOURCE IN THE BASE 8 Claims, 6 Drawing Figs.

[52] US. Cl 324/34 TK, 162/198, 162/263 [51] Int.CI GOIr 33/12 [50]Field of Search 324/34 TK; 1 33/147 L,l47 N;73/159; 162/198, 263

[56] References Cited UNITED STATES PATENTS 1,946,924 2/ 1934 Allen eta1. 324/40 2,665,333 1/1954 Dunipace et a1 324/34 TK 3,411,075 11/1968l(ahoun'...'l..ll 3,513,555 5/1970 Vachon ABSTRACT: In an apparatus formeasuring the thickness of material including a magnetic sensor formingan incomplete magnetic circuit, a gas source, structure defining agas-confining chamber in communication with said gas source providing agas cushion on the top surface of said material for supporting thesensor a fixed distance above the top surface of said material, andreadout means for producing a signal dependent on relative verticalsensor movement, the improvement comprising material support structureincluding a supporting member formed of magnetic material to complete amagnetic circuit with the sensor, and providing a flat supportingsurface located opposite the sensor and contacting the underside of thematerial, a suction source, and structure providing communicationbetween the suction source and the underside of the material adjacentsaid flat supporting surface to maintain the underside of the materialflush against the flat supporting circuit such that parameters of themagnetic circuit due to the distance between the sensor and the magneticsupporting member are dependent solely on the thickness of the material.

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OSCILLATOR R E m WA. Y L l a m M m T A C E m R 8 W O W a D VOLTAGEVOLTAGE MAGNETIC THICKNESS GAUGE WITH A GAS- SUPPORTED SENSOR AND ASUCTION SOURCE IN THE BASE This invention relates to measuring thethickness of material, and particularly to continuously measuring thethickness of a travelling web.

An object of the invention is to provide improved apparatus forcontinuously and accurately monitoring the thickness of material (suchas continuous webs of paper and the like), without hindering free travelthereof.

Another object is to provide structure of simple and economicalconstruction for supporting a travelling web during measurement of itsthickness, which serves as a magnetic reference of constant magneticproperties cooperating with a magnetic sensor to establish a magneticcircuit having its reluctance dependent on the thickness of thistravelling web, and which all the while firmly and snugly supports theweb during its travel past the magnetic sensor.

The invention features, in an apparatus for measuring the thickness ofmaterial including a magnetic sensor forming an incomplete magneticcircuit, a gas source, structure defining a gas-confining chamber incommunication with said gas source providing a gas cushion on the topsurface of said material for supporting the sensor a fixed distanceabove the top surface of said material, and readout means for producinga signal dependent on relative vertical sensor movement, the improvementcomprising material support structure including a supporting memberformed of magnetic material to complete a magnetic circuit with thesensor, and providing a flat supporting surface located opposite thesensor and contacting the un- I derside of the material, a suctionsource, and structure providing communication between the suction sourceand the underside of the material adjacent said flat supporting surfaceto maintain the underside of the material flush against the flatsupporting surface such that parameters of the magnetic circuit due tothe distance between the sensor and the magnetic supporting member aredependent solely on the thickness of the material.

In a preferred embodiment, communication between the suction source andmaterial is through apertures in the supporting member, arranged toinclude an area at least inclusive of the projected area of the gascushion chamber on the flat supporting surface; these apertures areperipherally spaced about an imaginary circle, enclosing the projectedarea of the gas cushion chamber on the flat perforated supportingsurface; where the material being measured is a continuous travellingsheet, the suction applied is sufficient to maintain the requisiteflushness between sheet and supporting surface without inhibitingoverall web travel; and, both the sensor and the material supportingmember are mounted on carriages movable across the width of the materialbeing measured, for measuring the thickness of different locations alongthe width.

Other objects, features and embodiments will appear from the followingdescription of a preferred embodiment of the invention, taken togetherwith the attached drawings thereof, in which:

FIG. I is an elevational view, partially broken away, of a portion of athickness gauging apparatus embodying the present invention;

FIG. 2 is a sectional view of the apparatus of FIG. 1, along line 2-2thereof;

FIG. 3 is an elevational view of the sensing head of the apparatus ofFIG. 1, along line 3-3 thereof, with the electromagnetic sensor removed;

FIG. 4'is an elevational view of the web support structure of theapparatus of FIG. 1, along line 4-4 thereof;

FIG. 5 is a sectional view of the sensing head and web support structureof FIG. 1; and,

F IG. 6 is a diagrammatic view of circuitry useful with the apparatus ofFIG. 1.

FIGS. 1 and 2 show a thickness gauging apparatus 10 having a housing 12slidably supporting sensing head carriage l4 and baseplate carriage 16on rod pairs 18, 20, respectively.

Sensing head carriage 14 has sliding blocks 22 which slide on rodpair18, and includes connecting structure 24 having an arm 28 constructed toengage a number of links of drive chain 30 for moving head carriage 14therewith. A lower chain track 32, and upper chain track 33 are bothsecured to housing 12.

As seen in FIG. 1, drive chain 30 is driven by sprocket wheel 34 whichis in turn (on a common shaft therewith) driven through sprocket wheel35 and drive chain 36 by motor 38 and transmission 39.

Baseplate carriage support 16 is similarly slidingly supported on rodpair 20 by sliding blocks 40, and has connecting structure 42, includingan arm -50 constructed to engage a number of links of drive chain 51 formoving base support 16 therewith. Lower chain track 53 and upper chaintrack 52 are both secured to housing 12. Drive chain 51 is driven bysprocket wheel 54 which is in turn driven through sprocket wheel 56 (ona common shaft therewith), connecting drive chain 58 and sprocket wheel60 in common with drive chain 30 by sprocket wheel 35, drive chain 36,motor 38, and transmission 39.

Sensing head carriage 14 further includes a pair of pivot.

bars 67, between which is rotatably fastened a mounting plate 68, whichhas a flange 70 at one end rotatably secured through a crank arm 71 to apiston rod 72, contained in a rotatable cylinder 74 defininga pressurechamber, cylinder 74 being rotatably secured between support members 75on carriage 14. Baseplate carriage 16 includes similar pivot bars 77,with mounting plate 78 secured therebetween, and having a flange 80rotatably secured through a crank arm 81 to a piston rod 82, containedin cylinder 84, which is rotatably secured between support members 85 oncarriage 16.

Referring to FIGS. 3 and 5, sensing head has a rounded bearing surface92 received into a cylinder 93 having an adjacent cylindrical bearingsurface 94; cylinder 93 is tightly secured within mounting plate 68 andis connected through a flexible hose 96 to a blower 98 and air filter100. Sensing head 90 is assembled from a number of pieces forming anintegral member 101 defining an air inlet passage 102, and an airdistribution chamber 104, which communicates through a perforated eightequally spaced 0.246-inch diameter holes 105) sensor mounting plate 106,with an annular cylindrical airconfining chamber 108 (outer diameter1.250inch). Cylindrical wall 109 defining chamber 108 terminates atannular bottom surface 110 (2% inches outer diameter). Annular disc 123,secured to member 101, has spacedapertures 124 for receiving rods 125,which are secured to mounting plate 68, slidably therethrough. Stops 126on rods are sized larger than apertures 124 so that, in the absence ofair flowing through chamber 108, member 101 will be supported by disc124 on stops 126. Sensor mounting plate 106 has a central aperture 127in which is tightly secured, for movement with the sensing head, aconventional electromagnet sensor 128, having electrical leads 129. Thesensing head and connected structure are surrounded bya housing 130 ofrectangular cross section having an opening 131 exposing the sensinghead.

Web support plate 132 has a cylindrical bore 133 in which is fastened aperforated disc 134, of ferrous material having, (e.g., 24 0.125-inchdiameter perforations 135 (having centers arranged on a 3-inch diameterimaginary circle) therethrough to an exterior web supporting surface136. Frustoconical suction chamber 138 communicates with perforations135 and, through a cylindrical connector 142 and a flexible hose 144,with a suitable suction-producing device 146 e.g. a vacuum pump). Websupport plate 132 is surrounded bya protective housing 147 ofrectangular cross section, having an opening 148 for exposing the platetherethrough.

As shown in FIG. 6, electromagnetic sensor 128 includes an electromagnet150 having a center pole piece 152, an annular pole piece 154, and acoil 156 wound around pole piece 152 and coupled by leads 129 to abridge circuit 160. The opposite magnetic plate 134 completes themagnetic circuit of coil I56.

The bridge circuit 160 includes a parallel branch formed by theseriesdconnected fixed impedance 162 and the variable bridge balancingimpedance 164 and a parallel branch formed by the series-connected fixedimpedance 166 and the coil 156. Oscillator 168 is connected to a remoteDC power source 170 and has its output coupled across the bridge circuit160 by transformer 172. Connected across the fixed impedances 162 and166 is a rectifier 174 which rectifies the AC output of the bridgecircuit 160 and feeds the resultant DC signal to an amplifier 176. Theoutput voltage e from the amplifier 176 is transmitted to a directcurrent meter 178 and to a differential amplifier 180. An adjustable DCvoltage source 182 feeds a constant voltage reference signal 2, into thedifferential amplifier 180. The difference between the output signal e,and the reference signal e is a difference signal e fed by thedifferential amplifier 180 into the amplifier 182 before measurement bythe DC meter 184. This electrical apparatus may be located, e.g., on topof housing 12 adjacent motor 38.

In operation, with no air supply to sensing head 90, the head will reston stops 126. To introduce a travelling web beneath the head, pistons 74and 84 are actuated to pivot the sensing head mounting plate 68 and theweb support mounting plate 78 to the positions shown in FIG. 2. Afterthe web has been fed between the sensing head and plate, the pistons arereversely actuated to position plate 68 and 78 as in FIG. 1. Air issupplied to sensing head 90, around the periphery of bearing surface 92,to create an air bearing therearound, maintaining bearing surface 92spaced from bearing surface 94. In addition, air passing through theholes 105 to air-confining chamber 108 and against the top surface ofweb 112, supports sensing head 90 a predetermined and constant distanceabove the web (advantageously, about 0.020 inch). Suction issimultaneously applied to the underside of web 112 through theperforations 135 in baseplate 134 to maintain the underside of the webflush against plate surface 136, thereby overcoming the tendency of theweb to flutter or lift off the supporting surface due to the constantairstream flowing out around the periphery of chamber 108. Perforations135 are arranged to surround entirely the projected area of annular aircushion chamber 108 on plate surface 136, so as to maintain at leastthat material directly adjacent chamber 108 flush against surface 136.Therefore the length of the magnetic circuit between poles 154, 156 andplate 134 will be due solely to the thickness of the web 112 passingbetween the sensing head and plate 134 and the constantly maintainedheight of the air cushion supporting the sensing head above the web.Thus, any variance in the reluctance of the magnetic circuit will be duesolely to fluctuations in the web thickness. The change in reluctance,also reflected as a change in the inductance of coil 156, will, then, beproportional to the web thickness. Thus, if the bridge circuit isinitially balanced for zero output voltage at zero sheet thickness,output voltage e will be proportional to sheet thickness so that aproperly calibrated meter 178 can provide a direct indication of webthickness. 4

The suction through plate 134 is adjusted so as to be sufficient toprevent flutter of the web without interfering with the travel of theweb through the apparatus. Meter 184 may be utilized to monitorcontinuously deviations in thickness of such a travelling web. Voltagesource 182 is adjusted to furnish a reference voltage e equal to thevalue of e,, at some predetermined (i.e., preferred) web thickness. Thenthe difference voltage a read on meter 184 will indicate deviation fromthe predetermined thickness norm whereas meter 178 will continue toprovide an absolute thickness measurement.

Since webs to be measured may be wider than baseplate 134 or air cushionzone 108, the entire sensing head and base supporting carriages 14, 16,respectively, may traverse the entire width of the web upon energizationof motor 38, chains and 51 being operated at the same speed byidentically sized sprocket wheels 34, 54. Transmission 39 may beconstructed and calibrated to reverse automatically the direction ofmovement of chains 30, 51 each time the entire width of the web has beentraversed. Thus, thickness variations both across the width and alongthe length of the web can be continuously monitored. Inasmuch as thesensor is always opposite the same portion of the supporting disc 134,the disc provides a fixed magnetic reference, and need notbe of constantmagnetic properties throughout its entire surface area.

Other embodiments will occurto those skilled in the art.

What is claimed is:

1. ln an apparatus for measuring the thickness of material, saidapparatus including a magnetic sensor forming an incomplete magneticcircuit, a gas source, structure defining a gas-confining chamber incommunication with said gas source providing a gas cushion on the topsurface of said material for supporting said sensor a fixed distanceabove and out of contact with said top surface, and readout means forproducing a signal dependent on relative vertical sensor movements theimprovement comprising material support structure including a supportingmember formed of magnetic material to complete a magnetic circuit withsaid sensor and providing a flat supporting surface located oppositesaid sensor and contacting the underside of said material,

a suction source, and

structure providing communication between said suction source and theunderside of said material through said flat supporting surface to applysuction at least to material located over an area of said flatsupporting surface inclusive of the projected area of said gas-confiningchamber upon said flat supporting surface in order to maintain saidmaterial flush against said area of said flat supporting surface, suchthat parameters of said magnetic circuit due to the distance betweensaid sensor and said magnetic supporting member are dependent solely onthe thickness of said material.

2. The apparatus of claim 1 wherein said supporting member includes aplurality of apertures therethrough extending between said suctionsource and the underside of said material providing said communicationtherebetween.

3. The apparatus of claim 2 wherein said apertures are arranged toinclude said area.

4. The apparatus of claim 3 wherein said perforations are peripherallyspaced about an imaginary circle enclosing the projected area of saidgas-confining chamber on said supporting surface.

5. The apparatus of claim 4 wherein said gas-confining chamber is ofannular construction, and said perforations are located entirely outsideof the projected annular area of said gas-confining chamber on saidsupporting surface.

6. The apparatus of claim 1 wherein said material is in the form of acontinuous sheet travelling between said sensor and said supportstructure, and said suction source is constructed to apply suctionthrough said perforations sufficient to maintain the said underside ofsaid web flush against said supporting surface, while permitting travelof said sheet along said flat supporting surface.

7. The apparatus of claim 6 wherein said sensor and said materialsupport structure are each mounted on a carriage, and said carriage isarranged for selected movement across the width of said sheet transverseto. the travelling direction thereof, whereby the thickness of materialsheets of width greater than the width of said flat supporting surfacemay be measured at preselected zones across said width.

8. The apparatus of claim 7 including a flexible suction hose betweensaid material support structure and said suction source, said hoseconstructed to permit transverse movement of said support structure onsaid carriage across the width of said sheet.

* I! i 0 i

1. In an apparatus for measuring the thickness of material, saidapparatus including a magnetic sensor forming an incomplete magneticcircuit, a gas source, structure defining a gasconfining chamber incommunication with said gas source providing a gas cushion on the topsurface of said material for supporting said sensor a fixed distanceabove and out of contact with said top surface, and readout means forproducing a signal dependent on relative vertical sensor movements theimprovement comprising material support structure including a supportingmember formed of magnetic material to complete a magnetic circuit withsaid sensor and providing a flat supporting surface located oppositesaid sensor and contacting the underside of said material, a suctionsource, and structure providing communication between said suctionsource and the underside of said material through said flat supportingsurface to apply suction at least to material located over an area ofsaid flat supporting surface inclusive of the projected area of saidgas-confining chamber upon said flat supporting surface in order tomaintain said material flush against said area of said flat supportingsurface, such that parameters of said magnetic circuit due to thedistance between said senSor and said magnetic supporting member aredependent solely on the thickness of said material.
 2. The apparatus ofclaim 1 wherein said supporting member includes a plurality of aperturestherethrough extending between said suction source and the underside ofsaid material providing said communication therebetween.
 3. Theapparatus of claim 2 wherein said apertures are arranged to include saidarea.
 4. The apparatus of claim 3 wherein said perforations areperipherally spaced about an imaginary circle enclosing the projectedarea of said gas-confining chamber on said supporting surface.
 5. Theapparatus of claim 4 wherein said gas-confining chamber is of annularconstruction, and said perforations are located entirely outside of theprojected annular area of said gas-confining chamber on said supportingsurface.
 6. The apparatus of claim 1 wherein said material is in theform of a continuous sheet travelling between said sensor and saidsupport structure, and said suction source is constructed to applysuction through said perforations sufficient to maintain the saidunderside of said web flush against said supporting surface, whilepermitting travel of said sheet along said flat supporting surface. 7.The apparatus of claim 6 wherein said sensor and said material supportstructure are each mounted on a carriage, and said carriage is arrangedfor selected movement across the width of said sheet transverse to thetravelling direction thereof, whereby the thickness of material sheetsof width greater than the width of said flat supporting surface may bemeasured at preselected zones across said width.
 8. The apparatus ofclaim 7 including a flexible suction hose between said material supportstructure and said suction source, said hose constructed to permittransverse movement of said support structure on said carriage acrossthe width of said sheet.